1. Field of the Invention
This invention relates to the field of debris catchers and pressure relief valves for vacuum pumps and more particularly to the field of debris catchers and pressure relief valves for portable vacuum pumps for refrigeration systems.
2. Discussion of the Background
Refrigeration or air conditioning systems are typically closed systems that use a refrigerant normally mixed with a quantity of refrigeration oil. The oil in this regard is necessary primarily to maintain lubrication for the system's compressor and other moving parts. In use, a quantity of this oil inevitably ends up circulating in all of the system's flow paths (e.g., tubing) as it is carried along with the refrigerant. This includes in paths and parts of the pump where the refrigerant changes states (e.g., from liquid to vapor as it picks up heat and vapor to liquid as it gives up heat).
During service or repair of such refrigeration or air conditioning systems both large and small, the refrigerant is normally removed and captured and the system then typically opened up to atmosphere to perform the service work or part replacement. This process of opening the system up to atmosphere exposes all of the internal plumbing of the system to air and atmospheric moisture. Both of these compounds are very destructive to the efficient working of the normal refrigeration cycle of an operating system. Consequently, after the system has been repaired and closed back up, it is necessary to draw it into a deep vacuum (e.g., 500 microns) in order to completely remove all of the air, atmospheric moisture, and other contaminants prior to recharging the system with refrigerant. This evacuation process is critical and necessary as the refrigerant system will otherwise perform poorly if the recharged refrigerant is contaminated with air or other compounds including water vapor.
A common problem is that after a system has been evacuated and all of the refrigerant seemingly recovered and the system seemingly at atmospheric pressure, residual refrigerant will continue to bubble out of the system's remaining oil even in the case where a system has been left open to atmosphere for some time. This is similar to the carbon dioxide that continues to bubble out of a can of soda pop for quite some time as it sits open to atmosphere. Further, just as an open bottle of soda pop rebuilds pressure after the cap has been put back on, a refrigeration system builds up pressure once the system is resealed as the refrigerant bubbles out of the residual oil.
When a service technician then goes to hook up a vacuum pump to the system, he can be presented with a surprising condition. More specifically, he can find that the system he thought was at atmosphere or resealed at atmosphere has actually built up internal pressure above atmospheric pressure. Since vacuum pumps are typically not designed to handle being hooked up to pressure above atmosphere, the technician can be quite startled to find oil blowing out of the top of his vacuum pump as the built up pressure in the system enters and is then released through the inner workings of the vacuum pump. Additionally, the built up pressure in the system to be evacuated may blow the vacuum pump oil out of its sump as well as blow contaminating refrigerant oil from the system into the vacuum pump. The result is that the vacuum pump must or at least should be thoroughly cleaned and refilled with new and relatively expensive vacuum pump oil; otherwise, it will not efficiently work to draw down the system to a deep vacuum (e.g., 500 microns) or at least not do so in a relatively short period of time.
That is, vacuum pump oil in this regard is quite different from refrigerant oil. More specifically, a vacuum pump relies on highly refined special oil to make critical seals in the mechanics of the pump at deep vacuum levels. This oil must have a very low vapor pressure as it cannot boil or outgas at low pressures under vacuum or it will cause the vacuum pump to perform very poorly or even fail. This oil must be keep very clean and dry in order for the vacuum pump to operate well (e.g., pull a deep vacuum in a relatively short period of time). Refrigeration oil, on the other hand, is designed to lubricate and mix well with refrigerant. Refrigeration oil boils fairly readily at moderate vacuums and also tends to absorb many other volatiles like refrigerant, water, and solvents making it even worse for mixing in and essentially ruining the vacuum pump oil.
Most manufacturers of vacuum pumps recommend that the oil be changed in the vacuum pump prior to each and every use. Many technicians actually change the oil several times during large jobs as the oil becomes contaminated with compounds coming out of the system being evacuated such as water vapor, refrigeration oil, and acids. Contaminated vacuum pump oil as indicated above will quickly be rendered inefficient causing very slow evacuation times and/or an inability to draw a desired deep vacuum. In this last regard, it is not uncommon for a service technician to have to run an efficiently operating vacuum pump on a large system (e.g., the frozen food cases in a supermarket or an air conditioner for a hospital or office building) for 3 to 5 days continuously in order to properly draw it down prior to recharging the system with refrigerant. If the pump is not effectively operating, this length of time can be greatly extended potentially causing significant productive and financial losses (e.g., food spoilage or the need to shut down the hospital or office building). It may even cause the system when recharged to fail in short order if the evacuation was not deep or thorough enough.
With this and other problems in mind, the present invention was developed. In it, a combination debris catcher and relief valve is provided at the inlet upstream of the main body of the vacuum pump. In this manner, potentially contaminating debris is continuously caught and prevented from entering and damaging the pump. Additionally, any potentially damaging incoming fluid at pressure above atmospheric is relieved so as not to harm the operating parts of the vacuum pump or otherwise reduce its efficiency.